Effectiveness of influenza vaccine among elderly people living in residential care homes during outbreak situations

by Lau, Tin-wai

Abstract (Summary)

(Uncorrected OCR)
Abstract of thesis entitled
"Effectiveness of Influenza vaccine among Elderly People living in Residential Care Homes during Outbreak Situations"
Submitted by
Dr. LAU Tin-wai
For the Master of Public Health
at The University of Hong Kong
August 2005
Purpose
To assess the effectiveness of influenza vaccination in preventing influenza illness, hospitalization, pneumonia and death among elderly people living in residential care homes (RCHE) during influenza outbreaks in Hong Kong.
Background
Since 1998, the Department of Health (DH) has started annual influenza vaccination programme for elderly people living in RCHE. DH also investigated influenza outbreaks in RCHE.
Methods
We defined an influenza outbreak in RCHE as >2 cases of elderly with influenza-like-illness (ILI) (i.e., fever >38 ? and sore throat or cough), >1 of which had laboratory confirmation of influenza A. We reviewed clinical and epidemiological data collected during investigation of influenza outbreaks in RCHE in 2004. For each outbreak, we compared the proportion of elderly people developing ILI, requiring hospitalization, pneumonia and death among vaccinated and unvaccinated residents using Chi-square/Fisher Exact test. Furthermore, we applied Mantel-Haenszel weighted method to calculate the pooled relative risk (RR) and 95% confidence intervals (CI) for influenza vaccination in preventing these outcomes.
Results
A total of 117 outbreaks were analyzed. Among vaccinated residents, the mean proportion of elderly people developing ILI, requiring hospitalization, pneumonia and
death was 8.2%, 4.2%, 0.5%, and 0.15% respectively. Among unvaccinated residents, the corresponding proportions were 9.8%, 4.8%, 0.7% and 0.21% respectively. The pooled RR for ELI, hospitalization, pneumonia and death among vaccinated residents was 0.69 (95%CI: 0.54, 0.87), 0.70 (95%CI: 0.58, 0.85), 0.38 (95%CI: 0.25, 0.59) and 0.48(95%CI: 0.02, 0.97) respectively. This translates to a statistically significant vaccine effectiveness of 31% in preventing influenza illness, 30% in preventing hospitalization, 62% effectiveness in preventing pneumonia and 52% in preventing death in influenza outbreaks.
Conclusion
Influenza vaccination in RCHE is associated with reduced influenza illness and hospitalizations during influenza outbreaks in these homes. The degree of vaccine effectiveness is comparable with studies in Western countries.